Creative Grids wins hands down. I am replacing Omnigrids for several years now with the C.Grids rulers, i like the visibility of the lines so much better. And they are a bit more non-skid. The 6x12 inch and the 6.5x6.5 ones are the most used. I also have a 12.5 x 12.5 someplace for squaring up but I measure and square up the *increments* of a block before final assembly, then just lay the 6x12 ruler over the block as I do the last seams, to make sure its what it should be.

I use Omnigrid but would gladly switch to Creative Grids when the time comes.
Most commonly used ones 6.5" square, 12" square, 24" x 6" and 12 x 6".
I could add the 8" square and 10 " square.
I don't think I'd like a one-do-it-all ruler. If there are a gazillion lines on it I don't want it.
I prefer to buy separate rulers for each task.

I like non-slippery rulers with clear THIN black lines. I think the lines on the
Omnigrid area little too thick IMHO. And I don't care for the yellow lines. It
just makes it more difficult to see.